1. Technical Field
This invention relates to platforms for ladders and, more particularly, to a motor driven lifting assembly for assisting a user to raise and lower an air-conditioning unit above a ground surface and along a ladder.
2. Prior Art
It is well known that ladders have been commonly used in order to carry a person or worker up or down along a building wall or other structure. Extreme difficulty is often encountered in lifting heavy objects to the top of a house, to a second or higher story of a building, or onto a roof. This can be accomplished with a crane, but the expense of using a crane is often prohibitive. For example, it would be too expensive to rent a crane in order to install a typical air conditioning unit on the roof of a private residence. In addition, it would be difficult and expensive to transport a large piece of equipment such as a crane to a job site.
One prior art example shows a lift apparatus for use with a ladder having two spaced upright stringers and a plurality of horizontal rungs bridging the stringers and spaced at a distance vertically from one another. The lift apparatus comprises a frame, a prime mover mounted on the frame and having a rotatable output shaft, and at least one pair of sprocket systems spaced apart vertically from each other. At least one of the sprocket systems is operatively coupled with the output shaft of the prime mover. An endless driving force transmitting mechanism can pass around the pair of the sprocket systems. A controller is provided for controlling the prime mover in such a manner as to selectively rotate the output shaft thereof in forward or reverse direction, or stop it. An operating mechanism is provided for causing a plurality of gripper elements to be engaged with the corresponding rungs of the ladder. The gripper elements are carried by the endless driving force transmitting mechanism and spaced at a distance substantially corresponding to that of the rungs of the ladder. A platform is secured to the frame for supporting an operator thereon. Unfortunately, this prior art example is designed to raise and lower an individual and is not designed for use in raising and lowering heavy inanimate objects.
Another prior art example shows a raising system for scaffolding, elevator cabins and the like which comprises a vertical stationary beam member from one side of which equally vertically spaced similar rack teeth are protruding, each tooth having a substantially horizontal straight top face, a framework guided for up and down movement along said beam member, a power driven shaft rotatably supported by said framework and carrying spaced radial supports, a series of parallel idle shafts extending between the supports, equally spaced from one another and radially equally spaced from the driven shaft, and a plurality of cylindrical roller assemblies rotatably mounted on the idle shafts and adapted to come in successive rolling engagement with the top faces of said teeth during upward or downward movement of said framework. Each roller assembly includes several rollers disposed side by side. Unfortunately, this prior art example is not designed for use in raising and lowering a heavy inanimate object in cooperation with a ladder.
Accordingly, a need remains for a system in order to overcome the above-noted shortcomings. The present invention satisfies such a need by providing an assembly that is convenient and easy to use, is lightweight yet durable in design, and assists a user to raise and lower an air-conditioning unit above a ground surface. The assembly allows a user to securely place a ladder upon a ground surface and safely raise an air-conditioning unit to a desired height easily and efficiently. Such an assembly allows an individual user to do the work of two or more people. The assembly greatly reduces the possibility of injury to an individual, or damage to an object, and allows a user to accomplish a task more quickly. The present invention is simple to use, inexpensive, and designed for many years of repeated use.